1. Field of the Invention
The present invention relates to a technology for preventing leakage of developer from the developing device.
2. Description of the Related Art
Various types of dry, single component developing devices have been proposed and put to practical use. In the developing devices, it is necessary to stably form a thin-film of developer on a developing roller, which is an extremely difficult task.
In an exemplary technique, a restricting member (for example, a metal blade) is arranged parallel to the developing roller with a narrow gap (nip) between the two. Developer contained in a developing device is then made to pass through this nip thereby stably forming a thin-film of developer on the developing roller. The developer on the developing roller is then charged and it is used to develop a latent image formed on a photosensitive element. Extra developer that remains on the developing roller after developing the latent image is then recovered back into the developing device.
In a typical developing device, a sheet-shaped seal member (for example, a polyethylene terephthalate (PET) or polyurethane sheet) is provided in order to prevent developer from leaking out from a space between a casing of the developing device and a developing roller. The seal member abuts with the developing roller via a thin layer of developer present on the developing roller when developer remains on the developer roller. This structure prevents developer from not only leaking out of the casing but also from being scraped off while the thin layer of developer on the developing roller passes via the seal member. If a conductive sheet material is used as the seal member, it can solve two purposes: provide the sealing function and electrically charge the developer present on the developing roller. However, it is important to appropriately determine for each apparatus a pressing force of the seal member on the developing roller, the width of the nip between the seal member and the developing roller, a contact angle between the seal member and the developing roller, and the like.
Japanese Patent Application Laid-open No. 2002-72675, for example, discloses a developing device having two seal members arranged at different locations and with a certain angle therebetween in a space between a developing roller and a casing.
Japanese Patent Application No. 3235938 discloses a technique of employing a central seal member and two end seal members to seal a space between a casing and a developing roller. The central seal member extends along the central part of the developing roller while the end seal members are arranged on the two longitudinal sides of the central seal member such that the end seal members overlap with parts of central seal member. Each of the end seal members has a cutting line at a position where the overlapping ends.
Japanese Patent Application Laid-open No. 2002-214906 discloses a developing device having a seal member and a pressing-force adjusting unit that adjusts a pressing force of the seal member on a developing roller.
Because a typical seal member must cover a space between a developing roller and a casing, and the space is generally long, the seal member is likely to be thin and elongated. This shape of the seal member can undesirably lead to undulation of the seal member. The undulated portions of the seal member can inhibit uniform contact between the developing roller and the seal member, thereby leading to developer leakage. When the sealing function thus fails to be ensured, in a worst case, not only developer can splash within the image forming apparatus but also developer can spill over onto neighboring photosensitive elements and transfer belts. This can lead to defective image formation.